1. Field of the Invention
The present invention relates to a technical field of information communication system and a method of a peer to peer (P2P) type, including a plurality of node devices, which are mutually connected through a network.
2. Discussion of Related Art
When identical information is transmitted to a plurality of terminal apparatuses, belonging to a network, a terminal apparatus on a sending side produces copies of the information as many as number of the terminal devices on the receiving side, and the information thus copied is sent to the terminal devices.
Further, there is known a technique (IP multicast) that a router corresponding to such a plurality of transmission destination terminal devices is intervened, and one information transmitted by the terminal device for transmitting information is copied at a branch point of a destination by the router, and such the information is transmitted to the plurality of terminal devices (vide, for example, Patent Document 1). This technique reduces load of a terminal device which transmits information.
In addition, there is a known technique by which terminal devices are divided into groups, a group management server is provided to each group, and information one by one is transmitted to each group so that the information is transmitted to all the terminal devices, belonging to each of the groups (vide, for example, Patent Document 2).
Meanwhile, a technique called peer to peer is attracting attention in recent years. In the peer to peer information delivery system, for example, in an overlay network which is logically configured by use of a delivered hash table (hereinafter referred to as DHT), each of node devices participating in the overlay network does not recognize link information (for example, IP address) of all the node devices, but retains only part of link information obtained on participation or the like, and data inquiry or the like is performed on the basis of such the link information.
In an overlay network thus structured, it is necessary that delivery of load is appropriately shared even when participation and withdrawal of node devices occur often. Non-patent Document 1 discloses a technique that enables to appropriately share load even when participation and withdrawal often occur.
Patent Document 1: Japanese Unexamined Patent Publication No. 2000-49822
Patent Document 2: Japanese Unexamined Patent Publication No. 2002-344477 (FIG. 9)
Non-patent Document 1: T. Oka, H. Morikawa, and Y. Aoyama, “Lightweight Load Balancing for Distributed Hash Tables”, Technical Report of the Institute of Electronics, Information, and Communication Engineers Feb. 5, 2004, No. 103 issue, No. 650, p. 7-12